Category Archives: Programming

Material related to computer programming.

Using PHP output buffering to read a file

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There’s a function in PHP called readfile which will read a file and send its contents to stdout. That can be handy, but it’s not much good to you if you want to read the content of the file into a string.

There’s a neat trick using PHP’s output buffering that enables you to read the content of a file into a string without printing anything on stdout, and it goes like this:

  // start an output buffer
  ob_start();
  // print the file to the output buffer
  readfile( $file_path );
  // get the contents of the output buffer
  $content = ob_get_contents();
  // cancel the output buffer
  ob_end_clean();

Bash aliases for listing hidden files

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I finally figured out the ls command to list hidden files, and decided to setup a ~/.bash_aliases file for the first time. My ~/.bash_aliases file is now:

alias l.='ls -d .[!.]*'
alias ll.='ll -d .[!.]*'

So I have an “l.” command which will list hidden files and directories, and an “ll.” command which will list the same information in detail.

Setting a default value if a bash variable is undefined

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Say you want to take an optional command line argument to your script. That means that maybe $1 is set to a value, or maybe it’s not. You can read out the value and assign a default in the case that $1 is not set using the syntax:

  variable=${1:-default-value}

Which will set $variable to “default-value” if $1 is not set.

Replacing new lines with nulls in bash

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If you have a list of file names separated by new lines, and you want to turn it into a list of file names separated by null characters, for instance for use as input to xargs, then you can use the tr command, like this:

  $ cat /path/to/new-lines | tr '\n' '\0' > /path/to/null-separated

I found a whole article on various ways to replace text on *nix: rmnl — remove new line characters with tr, awk, perl, sed or c/c++.

Extracting a single file from a tar archive

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You can use a parameter to the -x command line switch to tell the tar command that you just want to extract one particular file from the archive. For example:

  $ tar -x filename/to/extract -f tarfile.tar

You can use the -O command line switch in conjunction with the above to have the file’s contents printed on stdout rather than created in the file system.